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84
High speed and instantaneous phase
overcurrent protection (HSOC, IOC)
≥
⋅
I>>
1.3 Im in
Recommended minimum setting for the HSOC function is:
≥
⋅
I>>> 2 Imin
When settings are chosen: Check the reach of the overcurrent protection in A at mixi-
mum source impedance for ZA and minimum source impedance for ZB. If the reach is
insufficient some measures must be taken.
The protection function can be used for specific application only if this setting value is
equal to or less than the maximum fault current that the relay has to clear.
6HWWLQJ RI UHOD\ RSHUDWLQJ FXUUHQWV ,!! DQG ,!!!
If Is is the primary setting operating value of the function, then the secondary setting
current (Is
) is:
SEC
I
S EC
⋅
Is
------------- - Is
=
SEC
I
PRIM
where I
is the secondary rated current of the main CT and I
SEC
current of the main CT.
The relay setting value is given in percentage of the secondary base current value, I
associated to the current transformer input I1. The setting value is given from the for-
mula:
Is
SE C
⋅
I
=
-------------- - 100
set
I
1b
&KDSWHU
&XUUHQW
(Equation 29)
(Equation 30)
(Equation 31)
is the primary rated
PRIM
1b
(Equation 32)
,
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